It seems like https://support.mozilla.org/en-US/questions/984193 It did not start with 30.0 but I upgraded in the hope that it would solve the situation. Every time I open a new window FF hangs for a few seconds. It does not hang opening a new tab! I tried the steps described in the above topic but they did not work. if I open the console and type gSnippetsMap.clear() the result is undefined. If I type localStorage['snippets-last-update'] = 0 the result is [Exception... "Component is not available" nsresult: "0x80040111 (NS_ERROR_NOT_AVAILABLE)" location: "JS frame :: debugger eval code :: <TOP_LEVEL> :: line 1" data: no] There is no difference if I use "Show a blank page" or "Show my home page" where home page is set to "about:blank" for "When Firefox starts". BTW, I am using Windows 8.1